Control system



Feb. 17, 1942. w. L. McGRATH 2,273,281

CONTROL SYSTEM Filed July 11, 1938 Q WA /////////////////A 1 William L. m Grath attorney Patented Feb. 17, i942 CONTROL SYSTEM William L. McGratlI. St. Paul, Minn, assignor to- Minneapolis-Honeywell Regulato Company,

Minneapolis lilinm, a corporation of Delaware Application July 1 1, 193:, Serial No. 218,577 1': Claims. (01. 82-4) This invention relates in general to automatic controls and is more particularly concerned with automatic controls for systems utilizing a plurality of prime movers.

In large refrigeration systems it is desirable to utilize a number of independently driven com-.

pressors. For providing economy in operation and flexibility of control, it is desirable to utilize internal combustion engines for driving the compressors. Thus by varying the engine speed and the number of engines in operation, the compressor displacement may be varied over a very wide range. v

It is the primaryobject of this invention to I provide an automatic control system for refrigeration systems of this general character and which will automatically increase the speed of the first engine to a maximum and then start the second engine as the load increases. Thus as the cooling load on the system increases as evi-' denced by increased suction pressure, the speed of the first engine will be increased and then the second engine will be started,"this action being obtained by the use of a suction pressure responsive device. 7

One problem encountered in control systems of this nature is short-cycling of the second compressor. Thus as the suction pressure rises to a value at which the second compressor is placed into operation, this compressor will provide more displacement than is necessary due to the fact that the output of the second engine cannot economically be reduced below 25 per cent' of its pressor and additionally provides for a continuous unbroken range of compressor capacities from a minimum to the maximum.

Another object of my invention therefore is the provision of a control arrangement for a pair of prime movers which controls the prime movers in sequence and in which the control ranges for the two prime movers overlap.

A further object of this invention is th provision of a control system for span of internal combustion engines which varies the output of the engines in sequence and which utilizes a wide differential switching mechanism for placing the second engine into operation, this wide differential switching mechanism permitting slowing down of the second engine after it has been started without stopping the engine.

Another object of this invention is the provision of a sequential. control arrangement for a pair of prime movers which operates to first place one prime mover into operation and then to place a second prime mover into operation and which provides for reducing the capacity of the first prime mover when the second prime mover is placed into operation.

Other objects of this invention will become apparent from the following description and the appended claims. While this invention is particulariy adaptable to refrigeration systems uti- 80 lizing internal combustion engine, driven comcapacity. Thus when theisecond compressor is so ence is made to the following detailed descripplaced into operation, it will cause the suction I pressure to be reduced quickly to a value in placing the compressor out of operation and this tioned dimculty. In accordance with my inven--- tion,' I provide for sequential control of the two engines in accordance with suction pressure and arrange the suction pressure controlling means in a manner to causethe-operating ranges of the first andsecond engines-to overlap to a predepressors, the invention is applicable to-other types of systems and to other types of prime movers.

For a full disclosure of my invention, refer- 4 0 cordance with one form of my invention.

termined extent. With this arrangement,- when a the second engine is started, the reduction in suction pressure resulting-therefrom will cause the. speed of both engines toibe decreased an amount necessary to just balance the compressor displacement against the load. This arrangement eliminates short-cycling of the second com- Referring to the drawing, reference character I indicates an air conditioning chamber having a return or inlet duct 2 leading from a space being conditioned, and a fresh air inlet duct 3. The chamber I is connected to a'fan 4 which causes air to flow'through the chamber and to be discharged through a duct 5 to a space to be conditioned 6. Located within the conditioning chamber I is a direct expansion cooling coil I. This cooling coil forms a part of a refrigeration system including compressors 8 and 9 which are connected by pipes l0, II and I2 to acondenser I 3. This condenser, in turn, is connected by a liquid line" I4 to a thermostatic expansion valve 55 I5 located at the inlet of cooling coil 1. The outlet 01' this cooling coil is connected by a suction line 16 and pipes 11 and 18 to th compressors 3 and 9. The compressors 8 and 9, it will be noted, are connected in parallel relationship.

The compressor 9 may be driven by an internal combustion engine 19 which may be of the usual type including an exhaust manifold 20, an intake manifold 2|, a starting motor 22, and a generator 23. This engine is indicated as driving the compressor 9 through pulleys 24 and 25 over which run belts 26. The engine 19 may be provided with a suitable form of speed controller such as the throttle valve 21. This throttle valve is positioned through a suitable linkage by means I of a proportioning motor 28 which may be of the type shown and described in Patent No. 2,028,110, issued to Daniel G. Taylor on January 14, 1936. This type of proportioning motor is provided with control terminals indicated as R, B and W, and is adapted to assume intermediate positions depending upon the relative values of resistances connected between terminals R and B and R and W. Due to this characteristic, the proportioning motor 28 is adapted to be controlled by means of a potentiometer controller and will assume positions corresponding to the position of the potentiometer slider upon its resistance.

The'proportioning motor 28 in addition to actuating the throttle valve 21 also actuates an auxiliary switch 29 which is diagrammatically illustrated as comprising a switch carrier 30 which is adapted to be actuated by a lever 31 attached to the proportioning motor shaft. This switch carrier 36 carries a mercury switch 32 of thewide angle type. This mercury switch,

it will be noted, is bent at its center so as to require tilting through a considerable angle to cause its globule of mercury to travel from one end to the other. The purpose of this wide angle type switch 32 is to control the ignition circuit and an automatic starting circuit for the engine '19. While this auxiliary switch has been illustrated as taking the form or a mercury switch, it will be understood that this switch may take other forms, and may be provided with adjustments for varying the positions of the throttle valve at which the switch is opened and closed.

Referring now to the electrical circuit for the engine 19, this may be of any suitable type and is herein illustrated as of a type similar to that utilized in automobile engines. Reference char acter 33 indlicates an. automatic starting relay for controlling the starting motor 22. This relay may be of any suitable type and if desired may be of the type shown and described in the Loehr et al. Patent 1,773,913, dated August 26, 1930. This type of starting relay is adapted to energize the starting motor when the ignition circuit is closed and is provided with a control terminal 34 which is connected by a wire 35tothe mercury switch 32. This mercury switch, in turn, is connected by wires- 36, 31 and 38 to a storage battery 39. The, wire 35 is also connected to the engine ignition coil 40. It will be apparent that when mercury switch 32 is closed due to the proportioning motor 28 opening the throttle valve 21 to a predetermined position,

parallel circuits will'be established for energizing the ignition coil 40 and the relay 33. This energization of relay 33 will cause it to complete a circuit from storage battery 39 through wires 38, 31, terminal 41, terminal 42, and wire 43 to the starting motor 22. The engine will thus automatically be started upon closure of the mercury switch 32. When the engine starts, the

relay 33 will automatically deenergize the starting motor 22 and will maintain the starting motor 22 deenergized so long as the engine is in operation as evidenced by operation of generator 23. For this purpose the relay 33 is provided with a terminal connected by wire 43 to the generator 23. The wire 43 is also connected by a wire 44, reverse current relay 45, wire 46, and wire 38 to the storage battery 39 for charging this battery when the engine 19 is in operation. It will be apparent that when mercury switch 32 opens, the ignition coil 40 will be deenergized and alsothe relay 33 will be deenergized thus stopping the engine 19.

The compressor 8 is driven by means of an internal combustion engine 41 which is provided with a throttle valve 48, this throttle valve being positioned by a proportioning motor 49 which is of the same type as the proportioning motor 28 which operates the throttle valve 21. This proportioning motor also operates an auxiliary switch 50' which is also of the wid difierential type. This switch is arranged so as to open when the throttle valve 48 reaches substantially closed position and so as to close when the throttle valve is moved to a predetermined open position. This auxiliary switch 50 controls the energization of an ignition coil 51 and a starting relay 52 for the engine 41. This arrangement is exactly the same as for engine 19 previously described and accordingly is not described here in trated as including a bellows 56 connected by a tube 51 to the suction line 6. This bellows 56 actuates a bell-crank lever 58 having an actuat ing arm 59 and a control arm or slider 60 which cooperates with a resistance 61 and a contact strip 62 for forming a control potentiometer. The controller also includes a second slider 63 which cooperates with a resistance and a contact strip 65 for forming a second control potentiometer. The slider 63 is actuated simultaneously with the slider 68 by any suitable means such as an insulated link 66. When the suction pressure is below a predetermined value, the bellows 56 will be collapsed by the biasing action of spring 61 sufficiently to cause slider 63 to engage the left-hand end of resistance 64, the slider engaging the left-hand end of contact strip 62 at this time. As the suction pressure increases,

the bellows 56 will expand, thus causing movement of the sliders 68 and 63 to the right. Upon movement of the sliders to the right,- the slider 63 will traverse its resistance 64 while'slider' 60 merely travels on contact strip 62. Upon further increase in suction pressure, the slider 60 will traverse the left-hand portion of resistance 61 while the slider 63 will traverse the right-hand portion of the resistance 64. Then upon still further increase in suction pressure, the slider 68 will traverse the right-hand portion of resistance 61 while the slider 63 will traverse the contact strip 65.

The controller formed of slider 60, resistance 61, and contact strip 62 controls the proportioning motor 49 and is connected to this motor by wires 61, 68, and 69. The controller formed of slider 63, resistance 64, and contact strip 65 controls the proportioning motor 28. As the slider 63 moves to the right across resistance 64 the proportioning motor 28 will open the throttle motor 4! will open throttle valve 48 an amount proportionate to the movement of slider 60 onresistance 6i.

1 Operation With the part in the positions shown, the suction pressure is at an intermediate value as indicated by the slider 63 engaging the center of resistance 64 and the slider 80 engaging the lefthand end of resistance 6!. Due to slider Glengaging the center of. resistance 04, the proportioning motor 28 has positioned the throttle valve 21 at approximately half-open position. This has, permitted closing of the auxiliary switch 29 which causes operation of the engine It at half speed. Due to slider 60 engaging the contact strip 62, the propditioning motor 49 has completely closed the throttle valve 48 and also opened the auxiliary' switch 50 for maintaining the engine 4| out of operation. If the load upon the system decreases, less refrigerant will be evaporated within cooling coil I and this will cause the suction pressure to decrease This decrease in pressure will cause slider 63 to move to the left across resistance 64, thus causing the proportioning motor 28 to move throttle valve 21 towards closed position for decreasingthe engine speed. Thus as the load upon the system decreases, the speed of engine is will bedecreased. It will be apparent that as the load upon the system continues to decrease, the motor 28 will completely close throttle valve 21 and open the auxiliary .switch 29, thus placing the engine out of operation.

The engine will then remain at rest while refrigerant will continue to evaporate within cooling coil 1, this causing the suction pressure to increase. This will cause movement of the slider 63 to'the right across resistance 84 for opening the throttle valve 21. Due to the wide differential action of the auxiliary switch 23; this switch will not close immediately upon the throttle valve 21 beginning to open, but will remain open until the throttle valve 21 opens to a predetermined minimum position. When the suction pressure rises to a value suflicient for causing closing of the auxiliary switch 32, the engine It. will bereplaced into operation. Immediately upon the engine starting, the action of com-- engine It is operating at full speed, the proportioning motor 49 will have opened valve 48 sufflciently for closing auxiliary switch 50. This closing of auxiliary-switch 50 will place the engine 41 into operation for thus aiding engine IS in carrying the load. When engine 41 starts,

the additional action of compressor 8.-will cause the suction pressure to begin falling. At this time, the sliders M and it will both be traversing their respective resistances SI and 64. Thus as the suction pressure decreases, the slider 60 will move to the left upon resistance SI for slowing down engine-41, and the slider 63 will 'move to the left across resistance 64 for slowing down engine It. Due to the wide differential of the auxiliary switch 50, this switch will remain closed while throttle valve 48 is being shifted for slowing the engine 41. The engine 41 will therefore remain in operation even though the throttle valve 48 is being moved towards closed position. Due to this simultaneously slowing down of engines i9 and 41, the dropping of thesuction pressure due to the starting of engine 41 will be overcome and thus both engines will assume speeds for just balancing the compressor displacement against the prevailing load. Upon continued increase in the cooling load, it will be apparent ,that

the suction pressure will increase thus causing .the speed" of both engines to be simultaneously increased. After the speed of. engine H! has been increased to a'maxim'um, continued increase in cooling load will cause further increase in the speed of engine 41 for thereby carrying the cooling load.

From the foregoing description, it will be apparent that my invention provides for the sequential control of the pair of internal combus tion engines and which increases the speed of one engine to a maximum and then places the second engine into operation. second engine into operation will provide more cooling action than-necessary, the speeds of the first engine and of the second engine are decreased just enough so that the combined effect of the engines just carries the load. These results are obtained by the-use of sequentially actuated controllers for the two engines, the ranges of the sequentially actuated controllers being overlapped 'in' part for providing simultaneous cbntrolof both engines when the second engine has just been started.. This arrangement in which the speed of the first engine is reduced when the second engine is started, provides for pressor it will reduce the suction pressure which slider engages the resistance 6|, the proportioning motor 49 will begin opening the throttle valve motor 28 will open throttle valve 21 wider for increasing the speed of engine It. Due to the wide differential of auxiliary switch, this switch will not close immediately upon the throttle valve 48 beginning to open. Howevenwhen the suction pressure increases to a value at which the 48. At the same time, the proportioning operating the second engine at a reasonably high capacity while at'the same time providing for a smooth and unbroken range of power from a minimum to a maximum. This feature provides for operating the second engine over long periods of time instead of causing the second engine to continuously start and stop when the load upon the system is just slightly more than can be carried by one engine.

While I have shown anddescribed my invention as applied to a refrigeration system utilizing a pair of intemai combustion engine driven compressors, it will be apparent that my invention is of broader'scope and is applicable to-other types of systems and to other types of prime movers.- Also, while theinvention is illustrated as controlling only a pair 0% prime movers in sequence, it will be. understood that as many prime movers as necessary may be sequentially controlled by enlarging the control systems, As many modifications and adaptations of my invention will occur to those skilled in the art,-I desire As' the placing of the to be limited only by the scope of the appended claims.

I claim as my invention:

1. In a system of the class described, in combination, a first prime mover, a second prime mover, load condition responsive means,, a first controller for graduatingly varying the speed of said first prime mover, a second controller for starting and graduatingly varying the speed of said second prime mover, said first and second controllers being sequentially and partially overlappingly actuated by said condition responsive means in a manner to increase progressively the speed of one of said prime movers, and then to start and increase progressively the speed of said other prime mover upon increase in load.

2. In a system of the class described, in combination, a first prime mover, a second prime mover, a first controller for varying the speed of said first prime mover in accordance with variations in load as the load varies through a predetermined range and a second controller for varying the speed of said second prime mover as the load varies through a predetermined difierent range, the ranges of said first and secondcontrollers partially overlapping.

3. In a system of the class described, in combination, a first prime mover, a second prime mover, load condition responsive means for sequentially controlling said prime movers, said load condition responsive means including means for graduatingly varying'the speed of said first prime mover as the load varies through a predetermined rangejn a manner to increase the speed of said first prime mover upon increase in load, said load condition responsive means also including means for starting and graduatingly. varying the speed of said second prime mover as the load varies through a predetermined dinerent range, in a manner to increase the speed of said second prime mover upon increase in load, said ranges partially overlapping to provide for simultaneous variation in speed of both of said prime movers within a predetermined load range.

4. In a system of the class described, in combination, a first prime mover, a second prime mover, load responsive means for sequentially controlling said prime movers in accordance with variations in load, said load responsive means being arranged to increase the speed of said first prime mover to a predetermined maximum and then to place said second prime mover into operation, and means for appreciably reducing the speed of said first prime mover as soon as said second prime mover is placed into operation.

5. In a system of theclass described, in combination, a first prime mover, a second prime mover, load responsive means for sequentially controlling said prime movers in accordance with variations in load, said load responsive means being arranged to increase the speed of said first prime mover to a predetermined maximum and then to place said second prime mover into operation, and means for reducing the speed of said second prime mover to a value lower than its initial value while maintaining said second prime mover in operation. I

6. In a system of the class described, in combination, a first internal combustion engine, a

second internal combustion engine, a speed controller for-said first engine, a speed controller for said second engine, a starting circuit for said second engine, load condition responsive means for actuating said speed controllers in a manner 7 to first increase the speed of the first engine and then to increase the speed of the second engine, and switching means actuated with said speed controllers for closing said starting circuit when the speed of the first engine is increased to a predetermined value.

7. In a system of the class described, in combination, a first internal combustion engine, a second internal combustion engine, a speed controller for said first engine, a speed controller for said second engine, load condition responsive means for actuating said speed controllers in a manner toincrease the speed of said first engine as the load varies through a predetermined range,

and to increase the speed of said second engine as the load varies through a predetermined higher range, said ranges overlapping in part, an electric circuit for said second engine, and means for closing said electric circuit when the load increases to a predetermined value, and for maintaining said electric circuit closed until the load falls to a predetermined lower value.

8. In a system of the class described, in combination, a first pumping means, a second pumping means connected to said first pumping means, a first prime mover for driving said first pumping means, a second prime mover for driving said second pumping means, means responsive tothe pressure at a point in said system affected by both of said pumping means for controlling said prime movers, said pressure responsive means including means for graduatingly varying the output of said first prime mover as said pressure varies through a predetermined range, said pressure responsive means also including means for graduatingly varying the output of said second prime mover as said pressure varies through a predetermined diflerent range, said ranges partially overlapping to provide for simultaneous variation in output of both of said controllers through a predetermined intermediate load range, and said pressure responsive means being operative whenever said pressure lies within said predetermined ranges to control the respectiveprime mover regardless of what value said pressure previously has had.

9. In a refrigeration system, in combination, an evaporator, a first compressor connected to said evaporator for withdrawing evaporated refrigerant therefrom, a second compressor also connected to said evaporator, a first prime mover for driving said first compressor, a second prime mover for driving said second compressor, means responsive to the pressure of the evaporated refrigerant for controlling said prime movers, said pressure responsive means including means for varying the output of said first prime mover as said pressure varies through a predetermined range, and means for varying the output of said second prime mover as said pressure varies through a predetermined different range, said ranges partiallyoverlapping to provide for simultaneous variation in output of both of said compressors through a predetermined intermediate load range.

10. In a system of the class described, in combination, a first internal combustion engine, a second internal combustion engine, a first electric motor means for gradually varying the speed of said first engine, a second electric motor said load responsive devicefor controlling said motor ,means, and means actuated by said motor means for stopping and starting said engines.

11. In a system or the class described, in com- .bination, a first prime mover, a second prime said second prime mover, a motor for positioning said second controller, a control circuit for said first motor, a control circuit for said second motor, a first variable resistance type controllerin the control circuit of the, first motor, a second variable resistance type controller in the control circuit of said second motor, a load condition responsive controller, and means-controlled by said load condition responsive controller for actuating said variable resistance type controllers in. se-

quence.

12. In a system of the class described, in combination, a first prime mover, a second prime mover, a first controller for graduatingly varying the output of said first prime mover, a motor for positioning said first controller, a second controller for graduatingly varying the output of said second prime mover, a motor for positioning said secondcontroller, a first control means for sitioning said first controller, a second motor for positioning said second controller, a first control means for said first motor, a second control means for the second-motor, a device associated with said first control means for varying the position assumed by said first motor, a devic associated with said second control means for varying the position assumed by said second motor, load condition responsive means for graduatingly actuating said devices for thereby positioning said motors, an electric circuit for starting said second engine, switching means for controlling said electric circuit, means actuated when the load on the system increases to a predetermined value for actuating said switching means to start said second engine, and means for reducing the output of said first engine upon starting of said second engine.

15. In a refrigeration system, in combination,

an evaporator, a first compressor connected to said evaporator for withdrawing evaporated refrigerant therefrom, a second compressor also connected to said evaporator, a first prime mover said first motor, a second control means for said second motor, a device associated with said first control means for varying the position assumed by said first motor, a device associated with said second control means for varyingthe position assumed by said second motor, a load condition responsive controller, and means actuated by said load condition responsive controller for actuating said devices? in sequence.

13. .In a system of the class described, in combination, a first internal combustion engine, a second internal combustion engine, a first controller for graduatinsly varying the output of said first engine, a second controller for grad-' uatingly varying the output or said second internal combustion engine, a first motor ior positioning said first'controller, a second motor for positioning said second controller, a first control means for said first motor, a second control means for the second motor, a device associated with said first control means for varying the position assumed by said first motor, a device associated with said second control means for varying the position assumed by said second motor, load condition responsive means for graduatingly actuating saiddevices for thereby positioning said motors, an electric circuit for one of said engines, and switching means actuated by one of said motors for controlling said switching means.

14. Ina-system oi the class described, in combination, a first internal combustion engine, a second internal combustion engine, a first controller ior graduatingly varying the output of for driving said first compressor, a second prime mover for driving said second compressor, and load condition responsive means acting upon increase in load to first increase the output of said first prime mover, tostart said second prime mover, and to increase the output thereof upon continued increase in load, said load conditioncombustion engine for driving said first compressor, a second internal combustion engine for driving said second compressor, a controller for g'raduatingly varying the output of said first engine, a starting circuit for said second engine, switching means for controlling said starting circuit, and load responsive means for actuating I said controller and switching means in sequence,

said load responsive means reducing the output of the first engine when the second engine is started.

17. In a system of the class described, a first prime'mover, a second prime mover, load responsive means for gradually increasing the speed said first engine, a second controller for graduatingly-varyln the output of said second interlial combustion engine, a first motor formmover.

WILLIAM L. MCGRA'I'H.

of the second prime 

